Plasma reactor and method of determining abnormality in plasma reactor

Abstract

A plasma reactor is provided which does not require a high power supply voltage and can form a plasma with a necessary and sufficient average current density over the whole region between a pair of electrodes to efficiently modify a gas flowing between the electrodes. The plasma reactor comprises first and second electrodes positioned to face each other, a dielectric material placed between the two electrodes and an electrical power supply for applying an alternating or pulsed current to the two electrodes and generating a plasma in the gas passing through the gap between the two electrodes to thereby modify the gas. By setting the average current density Ird of the plasma generated in the gap so that it satisfies the formula 10 −4 A/cm 2 ≦Ird≦10 −1 A/cm 2 , a concentrated discharge and a barrier discharge are simultaneously generated, thus forming a plasma having a sufficient average current density Ird for the efficient modification of the gas over the whole region of the gap.

1 . A plasma reactor comprising a pair of electrodes facing each other, a dielectric material positioned between the pair of electrodes wherein a gap is formed between at least one of the electrodes and the dielectric material, and an electrical power supply for applying an alternating or pulsed current to the pair of electrodes, and generating a plasma in a gas passing through the gap between the pair of electrodes to thereby modify the gas, wherein the average current density Ird of the plasma thus generated satisfies the formula  
       10 −4  A/cm 2 ≦Ird≦10 −1  A/cm 2   
     
     
         2 . A plasma reactor comprising a pair of electrodes facing each other, a dielectric material placed between the pair of electrodes wherein a gap is formed between at least one of the electrodes and the dielectric material, and an electrical power supply for applying an alternating or pulsed current to the pair of electrodes, and generating a plasma in a gas passing through the gap between the pair of electrodes to thereby modify the gas, wherein the formulas  
       0.1 mm≦t≦2.0 mm 
       d+t≦5 mm 
       d/t≦5 
       are satisfied when the total size of the gap is d and the thickness of the dielectric material is t.  
     
     
         3 . A plasma reactor according to either one of  claim 1  or  2  wherein the dielectric material is not in contact with the electrodes.  
     
     
         4 . A plasma reactor according to  claim 3  wherein the amount a that the center of the dielectric material in the width direction, is offset from the midpoint of the distance between the pair of electrodes and satisfies the formula  
       0≦a≦0.5×(d/2). 
     
     
         5 . A method of determining abnormality in a plasma reactor having a pair of facing electrodes, comprising the steps of applying an alternating current to the electrodes for generating a plasma in a gas passing through the gap between the two electrodes to thereby modify the gas and monitoring the voltage or current waveform on the electrode, wherein the determination of abnormality is based on a change in the waveform of the voltage or current of the alternating current.  
     
     
         6 . A method of determining abnormality in a plasma reactor according to  claim 5 , further including the step of filtering the monitored voltage or current with a high-pass filter, wherein abnormality is determined if a spike-shaped abnormal waveform is detected when the waveform of the voltage or current of the alternating current is filtered by the high-pass filter.  
     
     
         7 . A method of determining abnormality in a plasma reactor according to  claim 5 , further including the step of comparing the waveform of the monitored voltage or current with a reference waveform, wherein abnormality is determined if a spike-shaped abnormal waveform is detected when the waveform of the voltage or current of the alternating current is compared with the reference waveform.